This invention relates to mixing apparatus, and has particular though not exclusive application to such apparatus for mixing liquids in relatively large containers, for example paints in intermediate bulk containers (IBC).
It is often necessary, prior to application or use, to mix the contents of large containers, in particular paint containers, to condition the paint for smooth and effective application.
Heretofore, such mixing has been achieved in a variety of ways all of which suffer from various disadvantages.
Impellers such as propellers comprising a plurality of spiral blades on a rotating shaft are commonly used. However, removal of the propeller after mixing invariably results in paint dripping from the propeller onto the outside of the container. Furthermore, the use of a propeller in anything other than a full container can result in considerable splashing of paint within and without the container, as well as undesirable entrainment of air into the paint by way of the central vortex created by the rotating propeller.
Impellers are conventionally inserted through the top of a container to effect mixing, and, as mentioned above, can create problems if the container is only partially full.
It has been proposed to achieve mixing by means of a unit attached to the bottom of a container and reacting with the contents of the lower regions of the container to create mass movement throughout the volume of the container which is effective even if the container is other than full.
More particularly the unit includes a disc extending transversely of the lower regions of the container and provided with a central aperture surrounded by a plurality a circumferentially spaced apertures adjacent the periphery of the disc.
A diaphragm below the disc is alternately moved upwards and downwards relative to the disc, the configuration of the apertures in the disc being such that, on upward movement of the diaphragm liquid is preferentially forced upwardly through the central aperture, and, on downward movement of the diaphragm, liquid is preferentially drawn downwardly through the peripheral apertures. Thus a swirling motion is created within the container which serves to mix the contents thereof.
Such equipment, although non-intrusive, is complex and expensive, the mixing effect being very dependent upon the frequency of movement of the diaphragm, and is only suited to cylindrical containers.
An alternative to the above equipment utilises a static funnel from which radiate a plurality of circumferentially spaced jet outlets, an air-operated double diaphragm pump creating mass movement of the liquid towards and away from the funnel. On movement of the liquid towards the funnel, the liquid is preferentially forced through the outlets to create jets of liquid within the lower regions of the container, and, on movement of the liquid away from the funnel, liquid is drawn down through the centre of the funnel, the overall system being such as to create a swirling motion within the body of liquid.
Such a static jet mixer has been found to create closed cells within the body of liquid which remain unmixed and in which there is considerable heat build-up. Overall, mixing is unsatisfactory.
It would be desirable to be able to provide mixing apparatus which overcame the problems of the prior art, and in particular which ensured effective mixing of the full volume of contained liquid in an economic and cost effective manner.
According to the present invention there is provided, for a liquid container, mixing apparatus comprising a hollow sleeve member for location in the lower regions of the container, a plurality of circumferentially spaced outlets being provided in the upper regions of the sleeve member, and pump means for creating a reciprocating flow of liquid applied to the lower regions of the sleeve member, characterised by, in the flow path of liquid from the pump means to the sleeve member, a transducer mechanism co-operating with the sleeve member and subjected to the reciprocating flow of liquid such as to rotate the sleeve member about its central longitudinal axis in dependence upon said reciprocating flow.
It will be appreciated that, with such an arrangement, and as a result of the rotation of the sleeve member, which is typically through 15xc2x0 for each pulse of liquid, the jets of liquid emanating from the outlets are each directed in continuously changing directions within the container, thereby ensuring thorough mixing of the liquid and avoiding the establishment of any substantially static regions of non-agitation within the liquid.
In one embodiment of the invention, the pump means comprise a double acting diaphragm pump, the reciprocating movement of the diaphragm creating a mass movement of liquid into and out of the container.
Preferably the transducer mechanism comprises a ratchet wheel secured to, to be rotatable with, the sleeve member, and one or more pawls adapted to engage the ratchet wheel and linearly movable by, in the direction of movement of, the reciprocating liquid.
Conveniently there are two pawls mounted on a carrier and engaging diametrically opposite teeth of the ratchet wheel, the reciprocating movement of the liquid resulting in reciprocating movement of the carrier and attached pawls, each such movement of the carrier resulting in consequential stepped rotation of the sleeve member, each step being in the same direction of rotation.
Preferably there are two diametrically opposed outlets from the upper regions of the sleeve member, each outlet being directed substantially radially from the sleeve member.
The sleeve member and associated transducer mechanism may be located wholly within the lower regions of the associated container to provide a non-intrusive mixing system.
Alternatively, the sleeve member may extend through an aperture in the container to locate the outlets therefrom within the lower regions of the container, the lower regions of the sleeve member and the transducer mechanism being external of the container to provide an intrusive mixing system.